Predicting airflow in naturally ventilated double-skin facades: theoretical analysis and modelling

Naturally ventilated double skin façade (NVDSF) utilizes solar radiation to introduce natural ventilation through a double-skin façade cavity with vents. It is an easy-to-implement green technology that can be widely applied to new or existing buildings. However, its implementation in buildings is still limited as the coupled radiation and natural convection pose challenges in predicting ventilation performance. Moreover, the diversity of real-life applications raises a great need for a universally applicable method that can account for realistic design factors. Hence, an in-depth theoretical analysis model is required to facilitate the application of NVDSFs in buildings. This study proposes two new analytical models for NVDSFs that can directly predict ventilation rates with simple inputs. Numerical simulations are also conducted to validate the developed analytical models. It demonstrated that the experimentally validated numerical model can offer accurate predictions of natural convection and radiation for the case that involved complicated environmental, structural, and material factors. Most importantly, the realistic scenarios, NVDSFs with exterior vent louvers are studied both analytically and numerically. Different optical properties from two glazing materials, regular glass and low-e glass, are also tested with the proposed analytical models. Through validation, the discrepancies of the predictions by the proposed analytical models are −5% to −9% for ‘no-louver’ NVDSF for two different glazing materials (i.e., regular and low-e glass), and 13%–27% for NVDSFs with adjustable louver angles 45°–150°.